A stock metal workpiece is typically fastened to a fixture, which is, in turn, mounted to the bed of a milling machine. A workpiece usually includes excess material which presents bolt holes that receive bolts for mounting the workpiece to a machining fixture. A machining fixture usually consists of a flat plate with a pattern of threaded bolt holes for receiving such workpiece mounting bolts. Typical prior art workpiece mounting bolts generally have standard hexagonal heads that usually project above the surface of a workpiece. Such protruding bolt heads present obstacles in the machining process. What is needed is a fastener for securing a workpiece to a machining fixture that has no protruding head.